In recent years, the polyphenylene ether resins (also sometimes referred to as polyphenylene oxide resins) have gained wider recognition as engineering thermoplastics which can be shaped into articles having good mechanical and electrical properties, and their use has been extended to form types of products ranging from household appliances to automotive parts and trim, and so forth. The polyphenylene ether resins and methods of their preparation have been thoroughly described in the patent literature, including U.S. Pat. Nos. 3,306,874 and 3,306,875 (to Allan S. Hay), and U.S. Pat. Nos. 3,257,357 and 3,257,358 (to Gelu S. Stamatoff), and elsewhere.
As is well established, the polyphenylene ether resins are utilizable in admixture with styrene polymers over a broad spectrum of proportions, and the resulting blends can be molded into many of the same articles as above, but with the advantage that the moldings often possess better physical or chemical properties. Compositions of polyphenylene ether resins and styrene polymers are also described in the patent literature, including U.S. Pat. No. 3,383,435 (to Eric P. Cizek), and other patents known to those skilled in the art.
Compositions of polyphenylene ether resin and styrene polymers are normally flame retardant, and there are instances when it is desirable to impart a degree of flame retardancy to the compositions such that the molded articles are better able to resist burning or melting when exposed to elevated temperatures or placed near an open flame. To this end, it has been disclosed in the art that certain halogenated compounds, and brominated compounds in particular, are effective as flame retardant additives for polyphenylene ether-polystyrene blends. An example of such a disclosure is U.S. Pat. No. 3,809,729 (Reinhard). A drawback of brominated flame retardant additives, however, is their poor stability upon exposure to ultraviolet light radiation. This can be a serious problem if the flame retardant blends are to be manufactured into articles which during normal use are exposed to sunlight. After a time, discoloration and loss of flame retardancy can result.
It has been disclosed that blends made up of polyphenylene ether resin and copolymers of styrene and monobromostyrene have better flame resistance and UV-stability than corresponding blends of polyphenylene ether and polystyrene containing the same amount of bromine in the form of low molecular weight brominated additives. Good mechanical properties, especially Izod and Gardner impact strengths, are obtained with those copolymers which are compatible with the polyphenylene ether resin, that is, copolymers having up to about 70 percent by weight of bromostyrene content. Blends of this type are described by Glenn Cooper and Arthur Katchman in copending application Ser. No. 155,150, filed May 30, 1980. Other blends of a similar type containing a rubber modifier are described by the same authors in copending application Ser. No. 155,149, same filing date. Both of these applications are assigned to the same assignee as herein.